1. Field of the Invention
The present invention relates to an ink jet printing apparatus and an ink jet printing method which allow a print head to perform scanning for printing.
2. Description of the Related Art
An ink jet printing apparatus of the serial scan type moves the print head in a forward direction and a backward direction, while ejecting ink for printing. In this case, even with ink ejected at the same ink ejection start position, a position on a print medium impacted by ink varies between ink ejected in the forward direction scanning and ink ejected in the backward direction scanning. In bidirectional printing in which printing is performed both during the forward movement and during the backward movement to perform printing quickly, the moving direction of the print head during ink ejection is reversed between the forward movement and the backward movement. Thus, when the impact position is compared in each direction, ink ejected during the forward movement impacts the print medium away from the ink ejection start position in one direction. Ink ejected during the backward movement impacts the print medium away from the ink ejection start position in the opposite direction. Consequently, in view of this deviation, for droplets ejected at the same position, corrections need to be performed such that the ink ejected during the forward movement and the ink ejected during the backward movement impact the print medium at the same position.
In recent years, improved resolution has led to efforts to reduce the size of droplets. Thus, ink droplets ejected during a single shot are small and likely to be affected by the movement of the print head. As a result, the impact position on the print medium is likely to deviate. When the impact position of the ink droplet deviates depending on the scan direction of the print head, an image printed by the ink ejected during the forward movement of the print head fails to match an image printed by the ink ejected during the backward movement of the print head. Consequently, an undesired texture pattern may be formed in a printed image. Furthermore, the graininess of the printed image may be affected. Thus, when printing is performed, the impact positions of ejected ink droplets need to be accurately corrected.
As a technique for correcting the impact position, Japanese Patent Laid-Open No. H10-100398 (1998) proposes a printing apparatus which, before printing, adjusts the timing when a print head ejects ink, according to the scan speed of the print head and the distance between the print head and a print medium. In the printing apparatus, according to conditions set before printing, the timing for ink ejection is controllably corrected such that the ink is ejected to the desired impact position.
Furthermore, Japanese Patent Laid-Open No. 2004-314361 discloses a printing apparatus in which when a print head performs bidirectional printing, optical reading means reads a test pattern so that timings for ink ejection are adjusted according to the read information.
In the above-described printing apparatus, the correction amount for the temperature of the print head is calculated to be a preset coefficient so that a print mode and the ejection timing can be set before printing. Thus, the ink ejection timing is controlled in association with the temperature condition of the print head before printing. Consequently, ink is ejected according to the temperature of the print head measured before printing. As a result, printing can be achieved with the accuracy of the ink impact position kept high. However, the ink impact position cannot be accurately corrected in association with a variation in ejection speed or angle resulting from a variation in the temperature of the print head during printing.